1. Field of the Invention
This invention relates generally to the structure and fabrication process of a temperature probe. More particularly, this invention relates to the packaging structure and fabrication process for producing improve temperature probes that are more reliable for long term high temperature operation.
2. Description of the Prior Art
High temperature probes are still limited by the technical difficulties that the leakage currents are increased when operated at a high temperature high-voltage condition. Referring to FIGS. 1A to 1D for the structure of conventional temperature probes. In FIG. 1A, the temperature probe 10 includes a temperature sensing platinum chip 12 protected in a ceramic tube 20. The sensing platinum chip 12 is connected through two lead wires 14 to two fiberglass conductive wires 15 by welding at welding point 16. The fiberglass conductive wires 15 can sustain over high temperature. The lead wires 14 are insulated from each other by an insulation plate 17 inserted between the lead wires 14. Each of the fiberglass conductive wires wraps around a conductive line for conducting a resistance measuring current to the thin-film platinum chip 12 enclosed in the ceramic tube 20 for measuring a resistance that linearly increased versus a measured temperature. In FIG. 1B, a fiberglass tube 25 is further employed to wrap around the fiberglass conductive wires 15. Then, FIG. 1C shows a stainless steel tube 30 is employed to hold and protect the high temperature probe.
Referring to FIG. 1D for a zoomed cross section view of the interface between the fiberglass tube 25 and the ceramic holder 20. There is a small gap 35 at the interface where the fiberglass tube 25 contacts the ceramic holder 20. This small gap 35 generates a high differential voltage space between the conductive fiberglass lines 15 and the stainless steel holder 30. A leakage current is generated due to the high voltage difference between the fiberglass conductive lines 15 and the stainless steel since the stainless steel tube 30 is typically connected to a ground voltage. The leakage current may cause damages to the temperature probe. The high temperature probe has a reliability problem when operated in high temperature high-voltage condition. In order to prevent damages to the temperature probe, a transformer type of oven is provided to minimize the damages caused by the leakage current induced by high differential voltage. Transformer type of oven has a higher cost of production because additional electrical circuits have to be designed and manufactured as part of the oven.
Therefore, a need still exists in the art of manufacture and design of temperature probes to provide a new structural configuration for packaging and manufacturing the probes to overcome these limitations and difficulties. Preferably, the new configuration for manufacturing and packaging the temperature probes can assure the leakage current is maintained at a minimal level without being significant increased when the temperature is raised. Furthermore, it is desirable that the temperature probes can be reliably operated in a high temperature environment over long period of time without degradation.
It is therefore an object of the present invention to provide a new structural configuration and method of manufacture to provide a novel temperature probe with improved insulation and structural integrity at elevated temperature and high voltage operation condition. With this new and improved temperature probe, the aforementioned difficulties and limitations as that encountered in the prior art can be overcome.
Specifically, it is an object of the present invention to provide a new process for manufacturing and structural configuration where the ceramic tube for holding a temperature-sensing chip is wrapped with a layer of fiberglass to eliminate gaps vulnerable to high differential voltage discharge. The high temperature sustainable conductive lines connected to the temperature sensing chips are further wrapped by plastic insulation tube to minimize the leakage current As the operation temperature is raised over 500xc2x0 C. (Celsius), and the voltage is raised above 1250 VAC, the leakage current is kept below one milliampere (mA).
Another object of the present invention is to provide a new manufacture process and a packaging configuration to assure structural integrity of the temperature probe over long term high temperature operation. When the ceramic tube containing the thin-film platinum chip are protected and insulated with very small leakage current, the reliability of the temperature is improved.
Another object of the present invention is to provide a new manufacture process and a packaging configuration to improve the temperature measurement precision. When the ceramic tube containing the thin-film platinum chip and the conductive lines are protected and insulated with highly insulated covering layers, precision of temperature measurement is improved with a reduced leakage current.
Briefly, in a preferred embodiment, the present invention discloses a temperature probe. The temperature probe includes a temperature-sensing chip contained in a ceramic holder. The temperature probe is further connected to a pair of high-temperature sustainable conductive wires. The temperature probe further includes an electrical insulation layer wrapping over the ceramic holder and the high-temperature sustainable conductive lines such that the vulnerable gaps subject to high differential voltage discharges are eliminated. The problem of leakage current is resolved.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.